1. Field of the Invention
The present invention relates to a removable medium (information record medium) and to a drive (information read/write apparatus) for writing information to the removable medium and/or reading information stored on the removable medium.
2. Description of the Related Art
Recently, contents such as texts, still images, movies, music, programs recorded on removable medium such as compact disks (including CD-R, CD-RW and others), DVD (including DVD±R, DVD±RW, DVD-RAM and others) and MO (Magneto Optical Disk) are sold. In order to protect copy rights of these contents such as movies, music and programs recorded on the removable medium, technologies for preventing rewrite (interpolation) of information against author's intentions and for preventing illegal copying by unauthorized third parties are devised. For example, music CD-ROM and others to which copy protection is performed fall under these technologies.
On the other hand, for removable medium and drives (apparatuses for writing information to the removable medium and/or reading information stored on the removable medium), research and development for the purpose of high-density recording and high-speed access are actively promoted. As part of these, hybrid-type removable medium such as concurrent ROMRAM (see Japanese Patent Application Laid-Open Pub. No. 1994-202820) having a ROM (Read Only Memory) unit which is not recordable and a RAM (Random Access Memory) unit which is recordable, partial ROM and drives corresponding to these removable medium are proposed.
FIG. 9 is a plan view illustrating the concurrent ROMRAM as an example of the hybrid-type removable medium. On a ROM area 101 and a ROM area 102, disk specification information, such as a media type, a serial number and frame information which is a minimum unit of recording, is recorded as ROM information by phase pit having concavity and convexity. On a user area 105 between the ROM area 101 and the ROM area 102, a ROM area 103 and a recordable RAM area 104 are formed in a superposed manner. In FIG. 9, the ROM area 103 and the RAM area 104 are shown such that these are concentrically arranged on different areas, but actually, magneto-optical recording film is formed on the ROM area 102 and the RAM area 103 is allocated on the magneto-optical recording film. Next, how the ROM area 103 and the RAM area 104 are formed in a superposed manner is described.
FIG. 10 is an explanatory diagram of a layer structure on a cross section of the concurrent ROMRAM. A polycarbonate substrate A, a dielectric film B, a magneto-optical recording film C such as TbFeCo, a dielectric film D, an Al film (reflective layer) E and a UV hardening film F as a protective layer are laminated. ROM information is fixedly recorded in phase pits PP and read utilizing optical intensity modulation. On the other hand, RAM information is recorded as magneto-optical records for which magnetization direction is reversed by irradiating a laser to the magneto-optical recording film to make a state that magnetization reversal tends to be initiated and applying a signal magnetic field and read utilizing the Polar Kerr effect in which reflective lights are changed depending on directions of magnetization on the magneto-optical recording film when a laser is irradiated to the magneto-optical recording film.
FIG. 11 is an enlarged view of a surface of the concurrent ROMRAM. As described in FIG. 10, ROM information is fixedly recorded in the phase pits PP, and RAM information is recorded by the magneto-optical records OMM along arrays of the phase pits PP. In this way, the ROM area formed by the phase pits PP and the RAM area formed by the magneto-optical records OMM are arranged in a superposed manner. In the above concurrent ROMRAM, the RAM function by the magneto-optical recording film may be held by the RAM area 101 and the ROM area 102 as well as a user area 105.
To the hybrid-type removable medium represented by the above described concurrent ROMRAM, advanced technologies for preventing rewrite (interpolation) of information against author's intentions and for preventing illegal copying by unauthorized third parties are proposed.
For example, according to Japanese Patent Application Laid-Open Pub. Nos. 2003-36595 and 2003-115163, an optical disk having a ROM area on which disk-specific information is recorded and a recordable RAM area is disclosed. Contents are recorded on either the ROM area or the RAM area. If contents recorded on the optical disk cited in the each patent document are copied to another optical disk, since information specific to the optical disk which is the copy destination and information specific to the disk which is the copy source are different, or since information specific to the optical disk is not recorded on the ROM area of the optical disk which is the copy destination from the beginning, contents recorded on the RAM area can not be used, and in this way, rewrite (interpolation) of information against author's intentions and illegal copying by unauthorized third parties are prevented. Further, according to the No. 2003-115163, the RAM area includes a security signature including a private key of a user, and when new contents are additionally recorded, authentication and encryption are performed based on a public key method via network.
However, in conventional cases, an area on which contents are recorded and an area on which information for limiting writing/reading of contents on the removable medium are physically different areas, and each area has been administered by a host computer (personal computer, server and others) controlling the drive via software. Therefore, for example, by analyzing I/O processes on the host computer side, information for limiting writing/reading of contents and its method could be found out, and as a result, by replacing it with software which includes ill-intentioned codes, contents could be interpolated or illegally copied.
In these cases, it is difficult to identify the interpolator and the like. Further, in conventional cases, since access to a physically different area is needed when writing or reading contents, a limiting factor of high-speed access, which is a purpose in removable medium and the drive, has been constituted.